In an audit of the Chicago Police Department’s compliance with its reporting infrastructure for crime stats, Inspector General Joe Ferguson found police "failed to count each victim in multiple victim crimes as a separate offense."

In the sample examined by the IG, that discrepancy resulted in a 24 percent undercount in victim offenses. The errors were found in the police department’s reports to the Illinois Uniform Crime Reporting program, which feeds into the FBI’s Uniform Crime Reporting system.

The police department also "erroneously excluded certain crimes committed against protected persons," the report notes, which led to under-reporting aggravated assaults by 5.7 percent and batteries by 3.2 percent.

“Data analysis is central to CPD’s pursuit of its critical public safety mission,” Ferguson said, noting the "integrity and reliability of crime statistics hinges on" accurate incident reporting from the field and accurately classifying and reporting the information once entered into the system.

In a test of the latter, Ferguson said his office observed some flaws in the data system but noted the system largely accounted for documented assault-related crimes.

Ferguson said the police department agreed with the findings and offered a "robust response" to the report. The department plans to review all aggravated assaults and batteries from 2012 and 2013 to ensure the accuracy of its reports to the reporting system and provide clearer guidance on multi-victim crime reporting in its Field Reporting Manual.

Ferguson called the department's response to the audit "an encouraging sign of an organization seeking to improve."

"We caution, however, that what is reported out is only as reliable as what is fed into the system from the field," he said. "Public confidence in crime statistics therefore also depends on the accuracy of field reporting, which we did not test.”